Stainless steel seamless pipe for oil well use and method for manufacturing the same

Abstract

A steel pipe is formed by performing pipe making of a raw material having a composition containing C: 0.05% or less, Si: 0.50% or less, Mn: 0.20% to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 14.0% to 18.0%, Ni: 5.0% to 8.0%, Mo: 1.5% to 3.5%, Cu: 0.5% to 3.5%, Al: 0.10% or less, Nb: more than 0.20% and 0.50% or less, V: 0.20% or less, N: 0.15% or less, and O: 0.010% or less, on a percent by mass basis, wherein Cr+0.65Ni+0.6Mo+0.55Cu−20C≥18.5 and Cr+Mo+0.3Si−43.3C−0.4Mn−Ni−0.3Cu−9N≤11 are satisfied and subjecting the resulting steel pipe to a quenching treatment to heat to a temperature higher than or equal to the A c3 transformation temperature and, subsequently, cool to a temperature of 100° C. or lower at a cooling rate higher than or equal to the air cooling rate and a tempering treatment to temper at a temperature lower than or equal to the A c1 transformation temperature.

The invention claimed is: 
     
       1. A stainless steel seamless pipe for oil well use, comprising a composition containing C: 0.05% or less, Si: 0.50% or less, Mn: 0.20% to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 14.0% to 18.0%, Ni: 5.0% to 8.0%, Mo: 1.5% to 3.5%, Cu: 0.5% to 3.5%, Al: 0.10% or less, Nb: more than 0.20% and 0.50% or less, V: 0.20% or less, N: 0.15% or less, O: 0.010% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, wherein the following formula (1) and the following formula (2) are satisfied,
   Cr+0,65Ni+0.6Mo+0.55Cu−20C≥18.5  (1)
 
   Cr+Mo+0.351−43.3C−0.4Mn−Ni−0.3Cu−9N≤11  (2)
 
 where Cr, Ni, Mo, Cu, C, Si, Mn, and N: content of each element (percent by mass). 
 
     
     
       2. The stainless steel seamless pipe for oil well use, according to  claim 1 , wherein the composition further contains at least one selected from the group consisting of Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less and W: 10% or less on a percent by mass basis. 
     
     
       3. The stainless, steel seamless pipe for oil well use, according to  claim 1 , wherein the composition further contains at least one selected from the group consisting of REM: 0.0005% to 0.005% Ca: 0.0005% to 0.01%, and Sn: 0.20% or less on a percent by mass basis. 
     
     
       4. The stainless steel seamless pipe for oil well use, according to  claim 1 , comprising a microstructure including 25% or less of retained austenitic phase and the remainder composed of martensitic phase on a volume fraction basis. 
     
     
       5. The stainless steel seamless pipe for oil well use, according to  claim 4 , wherein the microstructure further includes 5% or less of ferritic phase on a volume fraction basis. 
     
     
       6. The stainless steel seamless pipe for oil well use, according to  claim 2 , wherein the composition further contains at least one selected from the group consisting of REM: 0.0005% to 0.005%, Ca: 0.0005% to 0.01%, and Sn: 0.20% or less on a percent by mass basis. 
     
     
       7. The stainless steel seamless pipe for oil well use, according to  claim 2 , comprising a microstructure including 25% or less of retained austenitic phase and the remainder composed of martensitic phase on a volume fraction basis. 
     
     
       8. The stainless steel seamless pipe for oil well use, according to  claim 3 , comprising a microstructure including 25% or less of retained austenitic phase and the remainder composed of martensitic phase on a volume fraction basis. 
     
     
       9. The stainless steel seamless pipe for oil well use, according to  claim 6 , comprising a microstructure including 25% or less of retained austenitic phase and the remainder composed of martensitic phase on a volume fraction basis. 
     
     
       10. The stainless steel seamless pipe for oil well use, according to  claim 7 , wherein the microstructure further includes 5% or less of ferritic phase on a volume fraction basis. 
     
     
       11. The stainless steel seamless pipe for oil well use, according to  claim 8 , wherein the microstructure further includes 5% or less of ferritic phase on a volume fraction basis. 
     
     
       12. The stainless steel seamless pipe for oil well use, according to  claim 9 , wherein the microstructure further includes 5% or less of ferritic phase on a volume fraction basis. 
     
     
       13. The stainless steel seamless pipe for oil well use, according to  claim 1 , wherein the composition contains Nb: 0.30% or more and 0.50% or less. 
     
     
       14. A method for manufacturing a stainless steel seamless pipe for oil well use, comprising the steps of forming a steel pipe by performing pipe making of a steel pipe raw material having a composition containing C: 0.05% or less, Si: 0.50% or less, Mn: 0.20% to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 14.0% to 18.0%, Ni: 5.0% to 8.0%, Mo: 1.5% to 3.5%, Cu: 0.5% to 3.5%, Al: 0.10% or less, Nb: more than 0.20% and 0.50% or less, V: 0.20% or less, N: 0.15% or less, O: 0.010% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, wherein the following formula (1) and the following formula (2) are satisfied and subjecting the resulting steel pipe to a quenching treatment to heat to a temperature higher than or equal to the transformation temperature and, subsequently, cool to a temperature of 100° C. or lower at a cooling rate higher than or equal to the air cooling rate and a tempering treatment to temper at a temperature lower than or equal to the A c1  transformation temperature,
   Cr+0.65Ni+0.6Mo+0.55Cu−20C≥18.5  (1)
 
   Cr+Mo+0.3Si−43.3C−0.4Mn−Ni−0.3Cu−9N≤11  (2)
 
 where Cr, Ni, Mo, Cu, C, Si, Mn, and N: content of each element (percent by mass). 
 
     
     
       15. The method for manufacturing a stainless steel seamless pipe for oil well use, according to  claim 14 , wherein the composition further contains at least one selected from the group consisting of Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less, and W: 3.0% or less on a percent by mass basis. 
     
     
       16. The method for manufacturing a stainless steel seamless pipe for oil well use, according to  claim 14 , wherein the composition further contains at least one selected from the group consisting of REM: 0.0005% to 0.005%, Ca: 0.0005% to 0.01%, and Sn: 0.20% or less on a percent by mass basis. 
     
     
       17. The method for manufacturing a stainless steel seamless pipe for oil well use, according to  claim 15 , wherein the composition further contains at least one selected from the group consisting of REM: 0.0005% to 0.005%, Ca: 0.0005% to 0.01% and Sn: 0.20% or less on a percent by mass basis.